This invention is related to a method of making the heat resistant polyester which has reduced amount of the end carboxyl group.
It is well known that in improving the heat resistance of polyester, i.e., the resistance to hydrolysis and resistance to aminolysis at high temperature, an effective method is to reduce the amount of the end carboxyl group (hereinafter this will be written as (COOH). Various methods have been proposed on reducing the (COOH) of polyester and, among them, the method of reacting the polyester with an epoxy compound is known as the typical example. However, study of this method has shown that the addition of epoxy compound would reduce (COOH) but there arise the problems such as the reduction in the degree of polymerization and insufficient reactivity of some epoxy compound with the (COOH) of polyester which results in an unsatisfactory effect.